Evidence of increasing intra and inter-species transmission of Mycobacterium bovis in South Africa: Are we losing the battle?

Abstract

Tuberculosis caused by Mycobacterium bovis is recognized worldwide as a significant health risk in domestic cattle, farmed and wild animal species as well as in humans. We carried out spoligotyping and variable number of tandem repeat (VNTR) typing methods to characterize 490 M. bovis isolates from livestock (cattle, n=230; pig n=1) and wildlife species (n=259) originating from different farms and regions in South Africa, with the aim to further establish the genetic diversity of the isolates, study the population structure of M. bovis and elucidate the extent of interspecies transmission of bovine tuberculosis. A total of ten spoligotype patterns were identified, two of which were novel (SB2199 and SB2200) and reported for the first time in the literature, while VNTR typing revealed a total of 97 VNTR profiles. Our results showed evidence of clonal expansion for some ancestral strains as well as co-infections with two or three M. bovis strains on some of the cattle and game farms, which suggested independent introductions of infected animals from epidemiologically unrelated sources. Five spoligotypes and nine VNTR profiles were shared between cattle and wildlife. Our findings showed that besides cattle, at least 16 different animal species in South Africa are infected with bovine tuberculosis, and highlight a strong evidence of inter and intra-species transmission of M. bovis. Infection of the blue wildebeest (Connochaetes taurinus) with M. bovis is described for the first time in this report. This update in epidemiological information raises concerns that bovine tuberculosis has increased its spatial distribution in South Africa and is also affecting an increasing number of wildlife species compared to ten years ago.